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Experimental flow boiling characteristics of R134a/R245fa mixture inside smooth horizontal tube
Author: Guo Cong | Print | Close | Text Size: A A A | 2017-11-23

The flow boiling characteristics were experimentally studied in smooth horizontal tube for pure R245fa and one of its mixtures, R134a/R245fa with 0.82/0.18 in mass fraction, which was regarded as a promising working fluid for Organic Rankine Cycle (ORC). The flow boiling heat transfer coefficient and pressure drop for the two fluids were measured under different vapor quality, mass flux, tube wall heat flux and evaporating pressure. Correlation for predicting the flow boiling heat transfer coefficient was developed for the selected mixture based on the experimental data. The results indicated that the flow boiling heat transfer coefficients of the two working fluids went up with mass flux, heat flux and evaporating pressure under the experimental conditions. The mixture of R134a/R245fa with 0.82/0.18 in mass fraction had less pressure drop, but higher heat transfer coefficient than that of the pure R245fa. The absolute errors of 89% experimental data are within 10% of prediction of the present developed correlation for the mixture. The results may benefit the potential utilization of R134a/R245fa in ORC.

 

Conclusions

Mixtures are regarded as promising working fluids for ORC. The flow boiling heat transfer characteristics of a mixture of R134a/R245fa with 0.82/0.18 in mass fraction, as well as one of its components, pure R245fa, were investigated by experiment in a horizontal tube. The following conclusions can be acquired.

(1) The flow boiling heat transfer coefficients of the selected working fluids went up with the mass flux, heat flux and evaporating pressure under the experimental conditions, i.e., 280–469 kgs-1m-2 of mass flux, 15–43 kWm-2 of heat flux, 0.54–0.84 MPa of evaporating pressure for the mixture, and 256–414 kgs-1m-2 of mass flux, 15–34 kWm-2 of heat flux, 0.2–0.3 MPa of evaporating pressure for R245fa.

(2) The mixture of R134a/R245fa has less pressure drop and higher heat transfer coefficient than that of pure R245fa, which is beneficial for designing a more compact and effective evaporator for the ORC system.

(3) Correlation predicting the flow boiling heat transfer coefficient was developed for the mixture. The average absolute error and maximum error for the present experimental data calculated by the correlation are 5.3% and 14.2%, respectively. The absolute errors of 89% experimental data are within 10% of the correlation prediction.

 

The results have been published on Applied Thermal Engineering 103 (2016) 901–908.

 

 

The experimental setup. (a) Schematic diagram. (b) Experimental facilities.

 

 
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